Hydrorefining is performed in order to reduce the amount of sulfur, metals, and other such impurities in a heavy oil such as a petroleum residue. This hydrorefining is conducted by bringing the heavy oil into contact with a catalyst in the presence of hydrogen. Because heavy oils contain large quantities of metal, metal and coke build up on the catalyst through prolonged hydrorefining, and this steadily lowers the activity of the catalyst until there is substantially no catalytic activity at all, at which point the catalyst life is at an end. It is desirable in the hydrorefining of a heavy oil to further enhance the impurity removal performance and extend the service life of the catalyst. To this end, there have been studies into methods in which the performance of the hydrorefining catalyst itself is enhanced and, at the same time, a plurality of catalysts are used in combination.
In particular, there was no catalyst up to now that offered both good desulfurization characteristics and good demetalization characteristics. Accordingly, a hydrorefining reaction apparatus made use of a combination of two catalyst layers, consisting of a front catalyst layer packed with a catalyst having excellent demetalization characteristics, and a rear catalyst layer packed with a catalyst having excellent desulfurization characteristics. Unfortunately, it was difficult to achieve a good balance between demetalization characteristics and desulfurization characteristics, and to maintain this balance over an extended period, even if the amount of catalyst packed into the front and rear catalyst layers was adjusted.
No prior art has so far provided a hydrorefining method with which the impurity removal performance is adequately high and a long catalyst service life can be achieved. For instance, the impurity removal performance can be improved by raising the reaction temperature, but this accelerates the build-up of coke and so forth and quickly diminishes the activity of the catalyst, so stable operation over an extended period is impossible. Furthermore, the performance of the individual catalysts can be improved through modification of the hydrorefining catalysts, but when these catalysts are combined their performance is sometimes inadequate. Also, the demand for middle distillate products such as kerosene and gas oil is higher than that for heavy oils, so it is desirable to obtain a greater quantity of light oil through a cracking reaction that occurs simultaneously with the hydrorefining of a heavy oil.
The present invention was conceived in an effort to solve these problems encountered with prior art, and a first object thereof is to provide a catalyst with excellent demetalization characteristics and desulfurization characteristics. A second object of the present invention is to provide a hydrorefining method and a hydrorefining apparatus with which removal performance for impurities such as metals or sulfur is high and can be maintained high over an extended period, and with which a larger quantity of light distillates can be obtained.
A first aspect of the present invention provides a hydrorefining catalyst comprising a porous carrier and a hydrogenation active metal supported thereon, wherein the total volume of pores with a diameter of 60 nm or less is at least 0.5 mL/g; (i) the volume of pores with a diameter of 8 nm or less is no more than 8% of the total pore volume; (ii) the volume of pores with a diameter of 8 to 13 nm is at least 15% of the total pore volume; (iii) the volume of pores with a diameter of 13 to 18 nm is not more than 30% of the total pore volume; (iv) the volume of pores with a diameter of 18 to 30 nm is at least 35% of the total pore volume; and (v) the volume of pores with a diameter of 30 to 60 nm is no more than 10% of the total pore volume.
As indicated for the characteristics of catalyst #011 in FIG. 1, the catalyst of the present invention has a characteristic pore distribution having a relatively broad band over a pore diameter range of 8 to 30 nm. Accordingly to this characteristic pore distribution, the hydrorefining catalyst has excellent desulfurization characteristics as well as excellent demetalization characteristics, and it can be seen that the performance thereof is maintained over an extended period. Using this catalyst in a hydrorefining apparatus equipped with a plurality of catalyst layers allows the apparatus to operate at a high temperature than in the conventional apparatus without diminishing the desulfurization performance, and this also enhances the demetalization characteristics. Also, a greater quantity of light distillates is obtained because the cracking rate of the heavy oil is higher. It can also be seen that the carrier having the above pore diameter distribution as well as the catalyst provided therewith has excellent mechanical strength.
A second aspect of the present invention provides an apparatus for hydrorefining heavy oils, comprising a first catalyst layer; a second catalyst layer located downstream from the first catalyst layer and a third catalyst layer located downstream from the second catalyst layer; wherein the effective metal build-up amount of the demetalization reaction of the catalyst in the first catalyst layer is at least 70, the effective metal build-up amount of the demetalization reaction of the catalyst in the second catalyst layer is at least 50, and the effective metal build-up amount of the desulfurization reaction is at least 50. The combined volume of the catalyst in the first and second catalyst layers in the hydrorefining apparatus is at least 45% of the combined volume of the catalyst in the first to third catalyst layers, and the volume of the catalyst in the second catalyst layer is at least 10% of the combined volume of the catalyst in the first to third catalyst layers.
With the hydrorefining apparatus of the present invention, the first catalyst layer (upper catalyst layer) is provided with a catalyst having excellent demetalization characteristics, while the second catalyst layer (middle catalyst layer) is provided with a catalyst having excellent demetalization characteristics and desulfurization characteristics, so excellent demetalization characteristics and desulfurization characteristics can be maintained over an extended period. Also, a greater quantity of light distillates is obtained from this hydrorefining apparatus.
With the hydrorefining apparatus of the present invention, the catalyst in the first catalyst layer may be one that has a refractory porous carrier and a hydrogenation active metal supported on the carrier, and one in which (a) the volume of pores with a diameter of 50 nm or less is at least 0.4 mL/g as determined by nitrogen adsorption method; (b) the volume of pores with a diameter of at least 50 nm is at least 0.2 mL/g as determined by mercury intrusion porosimetry; and (c) the volume of pores with a diameter of at least 2000 nm is 0.1 mL/g or less as determined by mercury intrusion porosimetry. The catalyst in the second catalyst layer may be the above-mentioned inventive catalyst.
A third aspect of the present invention provides heavy oil hydrorefining method, comprising the steps of preparing a first catalyst layer, a second catalyst layer located downstream from the first catalyst layer and a third catalyst layer located downstream from the second catalyst layer; and bringing a heavy oil into contact with the first, second and third catalyst layers in the presence of hydrogen, wherein the effective metal build-up amount of the demetalization reaction of the catalyst in the first catalyst layer is at least 70, the effective metal build-up amount of the demetalization reaction of the catalyst in the second catalyst layer is at least 50, and the effective metal build-up amount of the desulfurization reaction is at least 50.